The present invention relates generally to encoder systems used for tracking movement of mechanical structures and, more particularly, to an analog encoder system and related method which facilitates proper position tracking even where the analog signals output by the encoder are distorted from an ideal.
Presently known analog encoder systems are often expensive due to the nature of the design, particularly due to the cost in manufacturing an encoder which will produce ideal analog output signals. Less expensive analog encoder systems, such as those using an encoder mask which is external to the photo sensors, may produce distorted analog output signals. For example, where the ideal analog output signals are triangle waves, less expensive encoder systems may instead produce more sinusoidal output signals which lack linearity throughout the entire signal.
It would be advantageous to provide an encoder system for tracking position even where the analog output signal of the encoder varies from the ideal.
In one aspect, a method for tracking movement of a structure utilizing first and second encoder output signals produced by an encoder system associated with the structure is provided. The first and second encoder output signals are out of phase with each other and amplitudes of the first and second encoder output signals repeatedly intersect each other near an upper intersection amplitude and a lower intersection amplitude. The method involves (a) tracking movement of the structure based upon the first encoder output signal when an amplitude of the first encoder output signal is within a range defined by the upper intersection amplitude and the lower intersection amplitude and an amplitude of the second encoder output signal is outside the range; and (b) tracking movement of the structure based upon the second encoder output signal when the amplitude of the second encoder output signal is within the range and the amplitude of the first encoder output signal is outside the range.
In another aspect, a method for tracking movement of a structure involves producing a first encoder output signal of varying amplitude. A second encoder output signal of varying amplitude is produced, the second encoder output signal out of phase with the first encoder output signal, the amplitude of the first encoder output signal and the amplitude of the second encoder output signal repeatedly intersecting over time near an upper intersection amplitude and a lower intersection amplitude. For a defined direction of the encoder, four cycle segments are defined, including: a first cycle segment during which the amplitude of the first encoder output signal falls within a range defined by the upper intersection amplitude and the lower intersection amplitude and the amplitude of the first encoder output signal is increasing; a second cycle segment during which the amplitude of the first encoder output signal falls outside the range and the amplitude of the second encoder output signal is increasing; a third cycle segment during which the amplitude of the first encoder output signal falls within the range and the amplitude of the first encoder output signal is decreasing; and a fourth cycle segment during which the amplitude of the first encoder output signal falls outside the range and the amplitude of the second encoder output signal is decreasing. Movement of the structure is tracked based upon the first encoder output signal during the first cycle segment and the third cycle segment. Movement of the structure is tracked based upon the second encoder output signal during the second cycle segment and the fourth cycle segment.
In a further aspect, an analog encoder system for tracking movement of a structure includes a first encoder output providing a first encoder output signal and a second encoder output providing a second encoder output signal. The first and second encoder output signals vary in amplitude as the structure moves, the first and second encoder output signals are out of phase with each other, and the first and second encoder output signals repeatedly intersect each other. A controller receives the first and second encoder output signals and tracks movement of the structure based upon the first encoder output signal when an amplitude of the first encoder output signal is within a range defined by an upper intersection amplitude and a lower intersection amplitude and an amplitude of the second encoder output signal is outside the range. The controller tracks movement of the structure based upon the second encoder output signal when the amplitude of the second encoder output signal is within the range and the amplitude of the first encoder output signal is outside the range.
In still a further aspect, an analog encoder system for tracking movement of a structure includes a first encoder output providing a first encoder output signal and a second encoder output providing a second encoder output signal. The first and second encoder output signals vary in amplitude as the structure moves, the first and second encoder output signals are out of phase with each other, and the first and second encoder output signals repeatedly intersect each other. A controller receives the first and second encoder output signals and tracks both a coarse position of the structure and a fine position of the structure. The controller tracks a coarse position over time according to a number of times an upper intersection amplitude and a lower intersection amplitude are crossed by the tracked encoder signal.
In another aspect, an analog encoder system for tracking movement of a structure includes a first encoder output providing a first encoder output signal and a second encoder output providing a second encoder output signal. The first and second encoder output signals vary in amplitude as the structure moves, the first and second encoder output signals are out of phase with each other, and the first and second encoder output signals repeatedly intersect each other. A controller receives the first and second encoder output signals and tracks a fine position of the structure by repeatedly switching back and forth between monitoring of the first encoder output signal and monitoring of the second encoder output signal.